OsbHLH5 Synergically Regulates Phenolamide and Diterpenoid Phytoalexins Involved in the Defense of Rice Against Pathogens

Int J Mol Sci. 2024 Nov 12;25(22):12152. doi: 10.3390/ijms252212152.

Abstract

Rice (Oryza sativa) produces phenolamides and diterpenoids as major phytoalexins. Although the biosynthetic pathways of phenolamides and diterpenoids in plants have been revealed, knowledge of their accumulation regulatory mechanisms remains limited, and, in particular, no co-regulatory factor has been identified to date. Here, using a combined co-expression and evolutionary analysis, we identified the basic helix-loop-helix (bHLH) transcription factor OsbHLH5 as a positive bifunctional regulator of phenolamide and diterpenoid biosynthesis in rice. Metabolomic analysis revealed that OsbHLH5 significantly increased the content of phenolamides (such as feruloyl tryptamine (Fer-Trm) and p-coumaroyl tyramine (Cou-Tyr)) and diterpenoid phytoalexins (such as momilactones A, momilactones B) in the overexpression lines, while their content was reduced in the OsbHLH5 knockout lines. Gene expression and dual-luciferase assays revealed that OsbHLH5 activates phenolamide biosynthetic genes (including putrescine hydroxycinnamoyltransferase 3 (OsPHT3), tyramine hydroxycinnamoyltransferases 1/2 (OsTHT1/2), and tryptamine benzoyltransferase 2 (OsTBT2)) as well as diterpenoid biosynthetic genes (including copalyl diphosphate synthase 4 (OsCPS4) and kaurene synthase-like 4/7/10/11 (OsKSL4/7/10/11)). Furthermore, we have demonstrated that OsbHLH5 is induced by jasmonic acid (JA), while pathogen inoculation assays indicated that the overexpression of OsbHLH5 in transgenic rice plants leads to enhanced resistance to Xanthomonas oryzae pv. oryzae (Xoo). Overall, we have identified a positive regulator of phenolamide and diterpenoid biosynthesis and have demonstrated that biotic stress induces phytoalexin accumulation partly in an OsbHLH5-dependent manner, providing new insights into the metabolic interactions involved in pathogen response and offering valuable gene resources for the development, through genetic improvement, of new rice varieties that are resistant to diseases.

Keywords: basic helix–loop–helix; diterpenoid; metabolic regulation; pathogen resistance; phenolamide.

MeSH terms

  • Coumaric Acids
  • Disease Resistance / genetics
  • Diterpenes* / metabolism
  • Gene Expression Regulation, Plant*
  • Oryza* / genetics
  • Oryza* / metabolism
  • Oryza* / microbiology
  • Oxylipins / metabolism
  • Phytoalexins*
  • Plant Diseases / genetics
  • Plant Diseases / microbiology
  • Plant Proteins* / genetics
  • Plant Proteins* / metabolism
  • Plants, Genetically Modified
  • Sesquiterpenes* / metabolism
  • Tryptamines / metabolism
  • Tyramine / analogs & derivatives
  • Tyramine / metabolism

Substances

  • Phytoalexins
  • Diterpenes
  • Plant Proteins
  • Sesquiterpenes
  • Tyramine
  • Oxylipins
  • feruloyltyramine
  • Tryptamines
  • Coumaric Acids

Grants and funding

This work was supported by the Project of Sanya Yazhou Bay Science and Technology City (SCKJ-JYRC-2022-06), the Hainan Provincial Natural Science Foundation of China (323MS019, 324QN196), the Project of National Key Laboratory for Tropical Crop Breeding (NO. PT2400008492), the “111” Project (No. D20024), Innovative Research Projects for Postgraduates in Hainan Province in 2023 (Qhys2023-240), the Hainan Provincial Academician Innovation Platform Project (HD-YSZX-202003), the Hainan University Startup Fund (KYQD(ZR) 1866), and Yazhou Bay National Laboratory team research funding.